Certain filling products include both liquid and suspended fibers or solids, such as pieces of fruit or cereals. When filling with such filling products, it is common to add a specific amount of solid matter into the container in a first step, and to then add liquid to fill the container. These two steps usually take place in two filling machines that operate separately from one another.
A common way to pre-proportion the solid matter is to use mechanical piston fillers. Given their piston/cylinder design and their very high degree of mechanical complexity, these fillers are not so easy to clean and sterilize. A particular disadvantage of the piston/cylinder is that it has sliding surfaces that can only be cleaned with a great deal of effort. In many cases, cleaning these sliding surfaces will require removing the entire piston. This means that during the cleaning procedure, it is not possible to sterilize with steam. This is because, since the system is open, it is not possible to build the pressure needed to make the steam hot enough to sterilize.